Magnetic levitation train is a high-speed carrier system. An extremely high accuracy supporting structure, i.e. guideway structure, is required when the train is running with high-speed. Firstly, for the force-bearing characteristics of the guideway structure, the deformation and the deflection of the guideway structure must be controlled within a very small range under the action of train dynamic load as well as under the influence of external environment, such as the influence of temperature variation, wind force action and etc., at the same time the dynamical characteristics of guideway structure must also be strictly controlled, the magnetic levitation train requires the first-order frequency of free vibration of the guideway structure must be greater than 1.1 times the ratio of train running speed to guideway structure span. Secondly, the running systems for magnetic levitation train also requires the functional zones of the guideway structure having extremely strict accuracies; the functional zones are at both sides of the top portion of guideway structure, inclusive of top sliding surface, gliding surface at both sides and bottom stator pack surface. The accuracies of all the above three function surfaces are required to be 1 mm or within 1 mm (0.4 mm). The above guideway structural requirement for the magnetic levitation train system determines that the guideway structure for magnetic levitation train differs greatly from that of the conventional railway bridge and track of ordinary low-speed and medium-speed carrier system.
It is known by structural calculation and analysis that in comparing it with conventional railway structure, the structure rigidity of guideway, which is able to satisfy the technical requirement for the running of magnetic levitation train, will increase a lot. Therefore classifying the guideway structure according to materials used for it, no matter steel structure or prestressed concrete structure or the reinforced concrete structure is adopted, the height, the width and the section dimensions of guideway structure must be increased greatly. The weight of magnetic levitation structure will also increase synchronously. Classifying the guideway structure according to construction system, there are two main modes of guideway construction, namely the monolithic construction and the layer construction mode. In monolithic construction mode, i.e. in an integration of the load-bearing structure and track-surface structure, according to the fabrication and connection style the monolithic construction mode of track and girder may be further classified into two cases. In the first case the track-surface functional zones and girder body are fabricated and processed as an integration structure and in the second case they are fabricated and processed individually and then connected together to be an integration structure. After the steel structure of functional zones and the main load-bearing girder of the former are integrally fabricated and processed, advanced six-axis NC (Numerical Control) boring-milling machine tool is used for integral machining of the top gliding surface, the lateral guiding surface and the connecting slot of steel girder for fixing stator packs are machined with the advanced six-axis NC (Numerical Control) boring-milling machine tool, finally the stator packs are installed. In the latter case the steel structure of functional zones, the function surfaces and etc. are fabricated and machined individually, the main load-bearing girder, pre-embedded elements and the connecting surface of the connecting elements are machined integrally under condition of an integral girder body, finally the steel structure of functional zones and the main load-bearing girder are connected as an integration after the machining work is completed. In both cases of above construction mode, the machining work of a whole girder is unavoidable. It is known from the material, construction composition, fabrication and machining of monolithic construction mode that although such a construction mode may provide a good integrity and a great structure rigidity, yet there is very high requirement for the general layout of the girder factory, the fabrication of formwork and the equipment of machine tools. The arrangement of the girder fabricating workshop must satisfy the requirement for a many of working procedures able to be orderly carried out at same time and a large thermostatic workshop is demanded for the machining work of a whole guideway girder. In case that the pre-stressed concrete hybrid girder is adopted, the formwork must have sufficient rigidity, enough to ensure the pre-embedded elements to be disposed respectively at accurate positions and the machine tool must be with six-axis numerical control ability. Thus high technical contents of equipment and a big investment are required. Therefore, a big engineering quantity is required because the supporting platform for machining the whole girder must basically be without any deformation. As for the layer construction mode, the load-bearing structure and the guideway-surface structure are fabricated separately, arranged layer by layer, and then connected to form a guideway structure by means of supporting structures.
Such a layer construction is also called a special construction. Its lower-layer is a conventional bridge structure system, its upper-layer is a wide guideway-surface structure of 6.192 meters long and 2.8 meters wide. The construction is composed of the body structure reinforced concrete plate girder and the top sliding steel plate and the guiding steel plate at the side of functional zone, side guiding steel plate as well as the bracket for fixing stator packs. Three reinforced concrete supporting posts are used for supporting the guideway surface and the lower-layer structure. The supporting posts are connected with the upper-layer structure with cement mortar bed poured on-site and fastened with steel screw rods. In case that the lower-layer structure is a concrete structure, the supporting posts may be directly connected with the lower-layer structure. Two of these three posts respectively at each of the external sides are with necking at the bottom portion thereof in order to achieve an effect of binge jointing. The main drawbacks of the structure are as follows:
1. When the steel structure of functional zones and the reinforced concrete plate girder are as a monolithic construction to be fabricated, shrinkage gaps are liable to occur at the connecting surface between two different kinds of material with different material properties, and the fatigue cracks will easily occur to shorten the service life of guideway structure.
2. The connection mode of the upper-layer and the lower-layer structure is unreliable. Hinge-crack caused by longitudinal expansion and longitudinal contraction due to temperature variation may occur at the bottom of the fore and the aft supporting post. Repeated load actions will make the crack to be developed and the reinforcing bar in hinge joint to be damaged and reduce the safety of the structure. Furthermore, in the case that the tie rods are used for the connection between concrete plate girder and posts, the circumstances of applied force are undefined, then the force applied on the cement mortar bed is complex. Thus the connection between the concrete plate girder and the posts is easily damaged when the longitudinal, the lateral and the vertical load act at same time, it will imperil the safety of the structure.
3. The adjustability of such supporting mode is poor because a part of the tie rod, which is used as the connection between the concrete plate girder and the posts, had been poured into the concrete plate girder and firmly cohered together with the concrete plate girder. In the position adjustment of the concrete plate girder of guideway-surface structure, a part of cement of the structure have to be chiseled away, so that it is more difficult in construction process and poorer in operating ability.
4. For the lateral rigidity of lower-layer structure is small, the lateral dimensions of the lower-layer structure have to be designed with a very large size in order to satisfy the dynamic characteristics requirement of the system.